1. Field of the Invention
The present invention generally relates to honeycomb structures, exhaust gas conversion apparatuses, and manufacturing method of the honeycomb structures.
2. Discussion of Background
Although many technologies have been developed in the field of conversion of exhaust gas of automobiles, sufficient measures may not have been taken for the conversion of the exhaust gas due to increasing traffic. Restrictions on the exhaust gas of the automobiles will become further strengthened. Particularly, restriction of NOx in the exhaust gas of diesel engines will become extremely strict. Conventionally, reduction of NOx has been made by controlling the combustion system of an engine. However, recently, this has not been sufficient.
As a NOx conversion system of the diesel engine corresponding to the above-mentioned problems, a NOx deoxidation system (called an “SCR system”) where ammonia is used as a deoxidant has been suggested. A honeycomb structure has been known as a catalyst carrier used for such a system.
The honeycomb structure has, for example, plural cells (through holes) extending from one of end surfaces of the honeycomb structure to another end surface in a longitudinal direction of the honeycomb structure. These cells are separated by cell walls where the catalysts are carried. Accordingly, in a case where the exhaust gas is introduced in the above-mentioned honeycomb structure, since NOx contained in the exhaust gas is converted by the catalyst carried on the cell walls, the exhaust gas can be treated.
It is normal practice that the cell walls of such a honeycomb structure are formed of cordierite and, for example, zeolite (formed by ion exchange with iron, copper, or the like) is carried as a catalyst in the cell walls. In addition to this, an example where zeolite is used for the cell walls so that the honeycomb structure is formed has been suggested (see, for example, International Publication No. WO 2006/137149 A1).
The entire contents of International Publication No. WO 2006/137149 A1 are incorporated herein by reference.